Full-space terahertz beam flexible steering coding metasurface based on topology optimization

In this paper, a full-space terahertz coding metasurface based on tunable materials and topology optimization is presented, which enables flexible steering of terahertz waves and enhances spatial utilization. First, the coding metasurface unit was topology optimized using the non-dominant sequencing genetic algorithm (NSGA-II) multi-objective optimization algorithm. By applying liquid crystal’s electrically tunable refractive index properties and the phase transition characteristics of vanadium dioxide (VO 2 ), the coding metasurface unit is capable of full-space 2-bit coding at a frequency of 0.70 THz. Then, based on the designed coding metasurface unit, the array arrangements of the coding metasurface are reversely designed to realize flexible beam steering in full-space. The results show that in the reflection space, single- and multi-beam steering can be realized at continuous arbitrary angles in the range of an elevation angle of 35° and an azimuth angle of 360°. Moreover, each beam’s elevation angle and azimuth angle in the multi-beam can be steered independently. In the transmission space, compared to the reflection space, it can not only flexibly steer single- and multi-beams, but also extend the steering range of the elevation angle to 40°, further enhancing the metasurface’s spatial utilization and the flexibility of terahertz wave steering. Therefore, the proposed terahertz coding metasurface can achieve flexible and reconfigurable beam steering in full-space and has potential applications in terahertz communication, phased array radar, and related fields.